Acid metal electroplating process and baths



United States Patent 5 Claims. 61. 204-45) This invention relates to a method and bath for producing uniform electrodeposits of metals. It also relates to a method for maintaining uniformity of electroplating bath compositions. It has been found that by using difiicultly-soluble, electroplating-active organic additives which form a heterogeneous phase in acid metal electroplating baths it is possible to achieve a self-regulation of the brightening elfect and other bath properties which may be influenced by the addition of organic agents.

Heretofore, electroplating-active additives, such as brightening agents, leveling agents, grain-reducing agents, porosity-prevention agents, equalizing agents and wetting agents,'have been added to the electroplating baths in the form of aqueous solutions having a certain concentration. During the operation of the electroplating baths a more or less pronounced consumption of these additives occurs. Therefore, if the consumed agents were not continuously replenished, the critical concentration, that is the concentration below which acceptable electrodeposits are no longer achieved, would soon be reached in the bath. The satisfactory operation of such electroplating bath, therefore, requires continuous analytical surveillance in order to maintain the concentration of the additives within the range necessary for achievement of satisfactory electrodeposits. In practice, however, this addition is in most cases accomplished on a purely empirical basis, that is after the lapse of certain time intervals and often only when the undesirable efiects become visible, which leads to products that must be rejected. Moreover, the periodic replenishment of electroplating additive agents may also lead to excessive concentrations in the cathode space because of insufiicient admixture, and this excessive concentration has an unfavorable effect upon the metal electrodeposit. In addition, there exists quite generally the danger of inadequate or excessive concentration of additives in the electrolyte solution, which may give rise to troubles of manifold types.

In contrast thereto, electroplating-active organic additives are used in accordance with the present invention which are difficultly soluble in the bath and form a heterogeneous phase. The electroplating bath is thereby continuously and in a-self-adjusting manner maintained near the saturation concentration of the additive component. If theconcentration of additives in the bath is reduced by normal consumption, the saturation concentration is again restored by the diificultly soluble substance lying on the bottom, so that further additions for the purpose of correcting the bath composition are not required during operation. Since the concentration of additives in the electrolyte remains constant, the bath does not require a continuous analytical surveillance. Consequently, in the baths compounded in accordance withthe present invention, the danger of an insutlicient orof an excessive electrolytes which are employed in each case.

of thick metal deposits such as those that are required in the production of rolled copper coatings and in the production of phonograph record matrices. The difiicultly soluble additives of the heterogeneous bath phase may be liquid or solid and in the latter case ordinarily form a bottom deposit. The solid agents may also be employed in electroplating baths which are continuously or periodically cycled with the aid of a pump. Under these circumstances, for example, they may be introduced by means of solution filters into the cycling pump line.

The substances employed as electroplating additives in accordance with the present invention are difficultly soluble organic compounds which are characterized by known groupings that bring about brightening, leveling, grain-improving or porosity-preventing effects. Such groups are, for example, nitrogen and/ or sulfur-containing groups, such as thiourea groups, dithiocarbamic acid groups, thioxanthogenic acid groups, trithiocarbonic acid groups, xanthogenic acid groups, thioimidazole or thiobenzimidazole groups, mercaptothiazole or mercaptobenzthiazole groups and other groups which contain a carbon atom attached only to hetero atoms, as well as azido groups, alkylene-diamine groups, polyamide groups and the like. These compounds may also contain watersolubilizing radicals, such as carboxyl groups and sulfonic acid groups, which form difficultly soluble metal salts with the heavy metal ions of the baths. Furthermore, the additives may contain the activating groups several times and in combination with each other, such as diificultly soluble compounds which contain simultaneously one or more thiourea groups and one or more dithiocarbamic acid groups.

Therefore, quite generally, dificultly soluble compounds with known electroplating-active groups may be employed for the baths according to the present invention. In many instances, therefore, it is possible to start from known brightening, leveling and other such substances which have been made difiicultly soluble by introduction of suitable substituents, such as aryl radicals. However, it is also possible to start from insoluble products with the above-mentioned active groups, and to render them soluble, for instance by an increase in the acid concentration of the bath electrolyte, or, in other instances, by addition of organic solvents, such as ethanol, isopropanol and the like.

It is advantageous if the saturation concentration of the difiicultly soluble agents amounts, as a rule, to at least twice the critical concentration of the agents. The saturation concentration of the additives employed in accordance with the present invention lies at about 0.5- 500 mg./l., especially 2-300 m=g./l., for the particular The maximum content of the additive in the electrolyte is determined by the upper limit of the saturation concentration, and an excess concentration is thereby avoided with certainty. As a rule, the critical concentrations amount to from one-half to one-eighth of the saturation concentration, so that even those baths which comprise only a saturation concentration of 50 or l2* /2% of additive still produce satisfactory metal electroplates. At a bath load of about 1 amp/l. the hourly consumption of additives amounts to about 3 to 16% of the differential quantities between saturation concentration and critical concentration (concentration tolerance range), whereby a certain operation reserve against unforseen incidents is provided and local inadequate dosing is excluded.

An advantageous embodiment of the process according to the present invention comprises placing the difficultly soluble agents into a solution filter which is inserted into the circulation pump line for a continuous bath filtration device. In order to avoid clogging of the solution filter by bath impurities, a contamination trap filter is inserted before the solution filter. The difficultly soluble additive may 'be admixed with kieselguhr, activated charcoal, special purpose fire clay and other porous masses, or in the case of liquid additive agents the porous materials may be saturated therewith. The permeability and incompressibility of the filter layer is thereby assured. The wettability of the solid difficultly soluble agent by the bath fluid may be improved by the addition. of wetting agents. In order to maintain the saturation concentration in the electroplating bath, it is in all cases suflicient to circulate the bath at the customary bath circulation rate of about one totwo bath volumes per hour, that is at the rate sufiicient to achieve an adequate continuous filtration.

The'process according to the present invention may be applied in conjunction with acid electroplating baths for copper, zinc, nickel, lead, tin and cadmium. The baths may be modified with customary wetting agents, such as the known ethylene oxide addition products to high molecular organic compounds with exchangeable hydrogen atoms, alkyl sulfates and the like. These wetting agents are soluble, but they are effective over a broad range of concentrations and therefore do not require close surveillance. vIf the difiicultly soluble additive is a brightening agent, whose leveling effect is insufficient, the leveling effect may be improved by simultaneously employing a leveling additive which is either in the form of a difiic-ultly soluble compound or also in soluble form. Of course, in the last-mentioned instance, the content of leveling agentin the bath requires surveillance. The agent must from time to time be replenished in accordance with its consumption. Accordingly, particularly advantageous are diflicultly soluble additives which perform several functions, that is, which simultaneously produce full brightness, a leveling effect and also possess a temperature tolerance which is sufficient for practical requirements. However, there are an entire series of technical electroplating processes in which a full brightening effect is not required and merely an increase in the fineness of the grain meets the technical requirements.

In those cases where the bath additive consists solely of the difficultly soluble additives according to the present invention and possibly also wetting agents, these baths can be operated completely without surveillance provided care is taken that the circulating pump filtration operates satisfactorily and the additives in the solution filterare replenished when necessary. Thus, it is not only possible to operate the baths in a considerably simpler manner but also in a more economical manner. By virtue of the self-regulation of the baths the production of imperfect products which must be rejected is practically completely eliminated.

. The following examples are given to illustrate the invention more clearly and to enable persons skilled in the art to better understand and practice the invention. The examples are not intended to be limitative.

Example I A bath having the following composition was used for acid copper electroplating: l

210 g./l. of copper sulfate, CuSO -5H O 120 g./l. of sulfuric acid 8 g./l. of the addition product of 8 mols of ethylene oxide to 1 mol of a coconut fatty alcohol mixture The bath was recycled and continuously filtered with the aid of a pump. A solution filter was inserted after the customary contamination trap filter; the solution fil ter contained, as the diflicultly soluble brightening agent, N,-N" di benzylthiocarbamyl-diethylene-triamine-N'-di- 4 thiocarbonyl-S-propane-w-copper sulfonate of the formula s orn-Nni-NH 1H2 3 H; s

\ HS(CH2)3SO3%CU At a recycling rate of one bath volume per hour, the

bath produced bright, smooth, bud-free and pore-free copper electrodeposits in a current density range of 0.5 to 8 amps/dm. at a temperature tolerance of 17 to 30 C. The leveling effect of the bath was sufficient to meet the requirements of many practical uses, so that the concurrent employment of other additives was not necessary. The saturation concentration of the brightening agent lies in thevicinity of 10 mg./l., and the critical concentration amounts to about 50% of the saturation concentration and therefore lies at about 5 mg./l. The consumption of brightening agent per ampere hour amounted to 0.8 mg, so that satisfactory operation of the bath was assured for up to 6 ampere hours per liter, even upon failure of the solution filter.'

Example 11 When an acid copper electroplating bath of the fol lowing composition 210 g./l. of copper sulfate, CuSO -5H O g./l. of sulfuric acid 8 g./l. of the addition product of 8 mols of ethylene oxide to 1 mol of a coconut fatty alcohol mixture C12 C18- was used and, analogous to Example 1, the solution filter was charged with pipera-zine-N,N bis-dithiocarbonyLS- propane-w-sodium sulfonate oft-he formula as the difiicultly soluble brightening agent, and the bath was recycled at a rate of one bath volume per hour, this bath produced bright, smooth, bud free and porefree copper electroplates within a current density range of 0.5 to 8 amps/dm. at a temperature tolerance of 17 to 30 C. The leveling effect of the bath was adequate for many areas of application even without the addition of special leveling agents. The saturation concentration of the difficultly soluble additive lies around 40 mg./l. and the critical concentration is about 25% of the saturation concentration and therefore lies at about 10 mg./l. At abrightening agent consumption rate of 1.2 mg./ampere hour, therefore, an operation reserve of 25 ampere hours per liter of the bath was assured.

Example III In conjunction with an acid copper electroplating bath having the same composition as that in Example 2, N- stearyl-dithiocarbamylS-propane-w-sodium sulfonate of the formula which had been produced by known processes, was inampere hour amounted to about 1.5 mg, so that the bath could remain operative for 17 ampere hours per liter even after failure of the circulating apparatus.

Example IV In conjunction with an acid copper electroplating bath composed of piperazine-N,N' bis-dithiocarbonyl-S-propionic acid sodium of the formula fix GET-CH2 S was charged as the difiicultly soluble brightening agent into a solution filter located downstream from a customary contamination trap filter. At a recycling rate of one bath volume per hour, the bath produced bright, smooth, bud-free and pore-free copper electroplates in a current density range of 0.5 to 8 arnps/dm. with a temperature tolerance of 17 to 30 C. At a saturation concentration of the difiicultly soluble additive of 30 mg./l., a critical concentration of about 12 mg./l. which amounts to 40% of the saturation concentration and a brightening agent consumption of 1.5 mg./ ampere hour, an operating reserve of 12 ampere hours per liter results for this bath.

Example V In conjunction with an acid copperplating bath having the same composition as the bath described in Example 4, thiazole-pyrazolone, which is known to be useful as a dye, was used as the solid brightening agent phase. At a recycling rate of one bath volume per hour, this bath produced uniform, clean, smooth, hard, but not brittle, pore-free and very fine-grain copper electroplates in a current density range of 0.5 to 8 amps/drn. with a temperature tolerance of 17 to 30 C. This bath was very highly suitable for galvano-plastic purposes. The saturation concentration of the difficulty soluble additive lies at about 96 mg./l., the critical concentration lies at about 12.5% of the saturation concentration and is therefore about 12 mg./l. At a consumption of 4 mg. of brightening agent per ampere hour, an operating reserve of 21 ampere hours per liter results for this bath.

Example VI 6 Example VII In conjunction with an acid copper electroplating bath of the same composition as the bath described in Example IV, the solution filter located downstream from a customary contamination trap filter was charged with a mixture consisting of the solid, difiiculty soluble brightening agent used in Example I and the difiiculty soluble leveling agent 1-benzyl-thiocarbamyl-Z-mercaptoimidazoline of the formula At a recycling rate of one bath volume per hour, this bath produced uniformly bright copper electrodeposits with good leveling characteristics in a current density range of 0.5 to 8 amps/dm. with a temperature tolerance of 17 to 30 C. The saturation concentration of the ditficulty soluble leveling agent amounts to 6 mg./l. and

the critical concentration lies at about 1.5 mg./l., which I corresponds to about 25% of the saturation concentration. From these values and based on a consumption of about 0.4 mg./l. per ampere hour, this bath has an operating reserve of 11 ampere hours per liter.

Example VIII sides in that the continuous surveillance is limited to the In conjunction with an acid copper electroplating bath cutly soluble 5,5-diphenyl-thiohydantoin of the formula,

( uHa)2= C=0 H1 1 IiIN which is an effective leveling agent. At a recycling rate of one bath volume per hour, this bath produced bright, smooth, bud-free and pore-free copper electroplates with good leveling characteristics in a current density range of 0.25 to 8 amps/dm. with a temperature tolerance of 17 to 30 C. The saturation concentration of the difi'icutly soluble leveling agent amounts to about 5 mg./l., the critical concentration to about 1 mg./l. which corresponds to 20% of the saturation concentration. At a consumption of about 0.4 mg. of leveling agent per ampere hour, this results in an operating reserve of 10 ampere hours per liter for this bath.

brightening agent which is effective over a broad concentration range, whereas the diflicult control of small amounts of the levelling agent is eliminated. At a recycling rate of one bat-h volume per hour, this bath produced bright and pore-free copper electrodeposits with good leveling properties in a current density range of 1 to' 8 amps/drn. with a temperature tolerance of 17 to 30 C. With a saturation concentration of the leveling agent of about 4 mg./l., a critical concentration of about 0.5 mg./l. (corresponding to 12.5% of the saturation concentration) and a consumption of about 0.2 mg. per ampere hour, an operating reserve of about 17 ampere hours per liter results for this bath.

Example IX In conjunction with an-acid copper electroplating bath composed basically of 210 g./l. of copper sulfate, CuSO -5H O 60 g./l. of sulfuric acid 35 C. This bath is very highly suited for the production of phonograph record matrices and other galvano-plastic purposes. The saturation concentration of the additive lies at about 70 mg./l. and its critical concentration amounts to about 6% of the saturation concentration, and therefore lies at about 4 mg./l. Based on a consumption of about 2 mg. per ampere hour, an operating reserve of 32 ampere hours per liter results for this bath.

Example X In Conjunction with an acid copper-electroplating bath composed of 210 g./l. of copper sulfate, CuSO -5H O 120 g./l. of sulfuric acid and 8 g./l. of the addition product of 8 mols of ethylene oxide to 1 mol of coconut fatty alcohol mixture C C the difliculty soluble brightening agent N-phenyl-thiocarbamyl-piperazine N dithiocarbonyl S propane-wcopper sulfonate of the formula 4 was used. At a recycling rate of one bath volume per Example XI An acid Zinc electroplating bath composed of 240 g./l. of zinc sulfate, ZnSO -7H O 2O g./l. of boric acid g./l. of aluminum sulfate, Al (SO l8H O 5 g./l. of sodium chloride and 1 g./l. of the sodium salt of the sulfate of an addition product of 4 mols of ethylene oxide to 1 mol of octyl alcohol was modified with N,N"-di-benzyl-thiocarbamyl diethylene-triamine-N-dithiocarbonyl S-propane-w-sodium sulfonate of the formula as the difiicultly soluble brightening agent lying at the bottom of the electroplating vessel. At a recycling rate of one bath volume per hour, this bath produced clean, pore-free and soft zinc electrodeposits in a current density range of L to 8 amps/dm. with a temperature tolerance of 17 to 30 C. and at a pH-value of the bath of 1.5 to 3.0. The saturation concentration of the difficultly soluble additive lies at about 18 mg./l., the critical concentration at about 7 mg./l., which therefore corresponds to about 39% of the saturation concentration. Based on a consumption of brightening agent of about 1.2 mg. per ampere hour, an operating reserve of 9 ampere hours per liter results for this bath. 4

8 Example XII An acid nicket electroplating bath composed of was modified with 4-butyl-5,6-benzocumarin of the formula as the diflicultly soluble leveling agent lying at the bottom of the electroplating vessel. In this bath only the leveling agent is self-regulating, whereas the dissolved brightening agent requires constant surveillance which, however, in view of its broad effective range, is without substantial importance. At a recycling rate of one bath volume per hour, this bath produced pore-free, ductile nickel electrodeposits with uniform brightness and leveling properties in a current density range of 1 to 8 amps/ dm. with a temperature tolerance of 45 to 60 C. The saturation concentration of the difficultly soluble leveling agent lies at 55 C. in the neighborhood of about mg./l. and the critical concentration at the same temperature is about 50 mg./l. Based on a consumption of about 10 mg. per ampere hour, an operating reserve of 10 ampere hours perliter results for this bath.

While I have set forth certain specific embodiments and preferred modes of practice of my invention, these are solely for purposes of illustration. It will be understood that the invention is not limited thereto and that various changes and modifications may be made in the invention without departing from the spirit of the disclosure and the scope of the appended claims.

I claim:

1. A self-regulating electroplating 'bath for the electrodeposition of metals capable of being electrodeposited from acid solution, said bath comprising (1) an acid solution of an inorganic salt of the metal to be electrodeposited, and

(2) a heterogeneous phase consisting solely of an auxiliary electroplate-improving organic addition agent which (a) is sparsely soluble in said acid electroplating bath, (b) has a saturation concentration of 0.5 to 500 mgm. per liter of electroplating bath liquid, and (c) has a critical concentration of about half of said saturation concentration, said addition agent being present in said bath in multiple quantities of said saturation concentration.

2. A self-regulating electroplating bath as in claim 1, which also contains a readily soluble auxiliary electroplate-improving addition agent.

3. The improved method of electrodepositing a metal capable of being electrodeposited from an acid electroplating bath in the presence of an auxiliary electroplateirnproving organic addition agent, which comprises electrodepositing said metal from a self-regulating electroplating bath comprising (1) an acid solution of an inorganic salt of the metal to be electrodeposited, and i (2) a heterogeneous phase consisting solely of an auxiliary electroplate-improving organic addition agent which 9 (a) is sparsely soluble in said acid electroplating bath, (b) has a saturation concentration of 0.5 to 500 mgm. per liter of electroplating bath liquid, and (c) has a critical concentration of about half of said saturation concentration, said addition agent being present in said bath in multiple quantities of said saturation concentration.

4. In a method of electrodepositing a metal capable of being electrodeposited from an acid electroplating bath in the presence of an auxiliary electroplate-impr-oving organic addition agent while continuously circulating said bath, the improvement which comprises contacting the circulating bath with a heterogeneous phase consisting solely of an auxiliary electroplate-improving organic addition agent which (a) is sparsely soluble in said circulating electroplating bath,

(b) has a saturation concentration of 0.5 to 500 mgm.

per liter of bath liquid, and

(c) has a critical cocnentration of about half of said saturation concentration, in multiple quantities of said saturation concentration.

5. In a method of electrodepositing a metal capable of being electrodeposited from an acid electroplating bath in the presence of an auxiliary electroplate-improving organic addition agent while continuously circulating said bath, the improvement which comprises circulating said bath through a solution filter containing a heterogeneous References Cited by the Examiner UNITED STATES PATENTS 1,003,092 9/1911 DOW et al. 20449 1,371,414 3/1921 Edison 20449 2,248,092 -7/ 1941 Korpium 20449 2,449,422 9/ 1948 Smith 20449 2,640,021 5/1953 Passal 20451 2,879,211 3/1959 Kardos et a1 204-49 2,885,399 5/1959 Omietanski 204- XR OTHER REFERENCES Kushner: Metal Finishing, September 1949, pp. 48-51 and 74.

JOHN H. MACK, Primary Examiner.

MURRAY TILLMAN, Examiner.

G. KAPLAN. Assistant Examiner. 

1. A SELF-REGULATING ELECTROPLATING BATH FOR THE ELECTRODEPOSITION OF METALS CAPABLE OF BEING ELECTRODEPOSITED FROM ACID SOLUTION, SAID BATH COMPRISING (1) AN ACID SOLUTION OF AN INORGANIC SALT OF THE METAL TO BE ELECTRODEPOSITED, AND (2) A HETEROGENEOUS PHASE CONSISTING SOLELY OF AN AUXILI-ARY ELECTROPLATE-IMPROVING ORGANIC ADDITION AGENT WHICH (A) IS SPARSELY SOLUBLE IN SAID ACID ELECTROPLATING BATH, (B) HAS A SATURATION CONCENTRATION OF 0.5 TO 500 MGM. PER LITER OF ELECTROPLATING BATH LIQUID, AND (C) HAS A CRITICAL CONCENTRATION OF ABOUT HALF OF SAID SATURATION CONCENTRATION, SAID ADDITION AGENT BEING PRESENT IN SAID BATH IN MULTIPLE QUANTITIES OF SAID SATURATION CONCENTRATION. 